1. Technical Field
The present invention relates to a drilling device and drilling method for drilling holes in drilled objects composed of stone materials, bedrock or other typically brittle materials such as concrete, asphalt, granite and marble, and more particularly, to a drilling device and drilling method suitable for use when drilling tiles and joints of tiled walls or use when drilling concrete walls laid on the inner surfaces of tunnels, sewer pipes and so forth.
2. Background Art
A method for reinforcing existing concrete walls consists of first cutting out a large portion of the wall, providing an iron brace in the cut out opening and then reinforcing the entire wall by solidifying this brace and an anchor arranged on the inner peripheral surface of the opening with concrete. At this time, the anchor is arranged by containing in a hole provided in the inner peripheral surface of the opening.
The hole for arranging this anchor is formed as shown in FIG. 11, for example, by a drilling device provided with a core bit 80 (drilling tool), composed by providing a tip-shaped bit 80a, which is formed by dispersing and arranging a cemented carbide or super abrasive in a binder phase comprised by sintering a binder, on the end of a cylindrical tool body, and a motor 81 (rotary drive device) for rotating this core bit 80 around an axis.
Namely, during drilling, a drilled object in the form of concrete 82 is drilled by pressing bit 80a provided on the end of core bit 80 against concrete 80 while rotating to form a columnar core 83a. By then extracting core 83 after braking off base 83a of core 83 remaining inside concrete 82, a hole having a diameter of, for example, about 15-50 mm and depth of about 50-500 mm is formed corresponding to the diameter of core bit 80.
In addition, in order to prevent collapse of a concrete wall laid on the inner surface of a tunnel, a hole is drilled through this concrete wall to bedrock on the back side of the concrete wall, and a grouting material and so forth is injected through this hole between the concrete wall and bedrock to reinforce the concrete wall.
When drilling into a concrete wall, conventional rock drills, which drill holes in bedrock, are not used because the vibrations generated by the rock drill act to promote collapse, and in their stead, a drilling device as shown in FIG. 11 is similarly used to drill concrete structures. In this case, holes having a diameter of, for example, about 70-100 mm are drilled corresponding to the diameter of core bit 80.
In addition, in order to prevent separation of tiles accompanying dilapidation of structures having tiled outer walls, holes are drilled in the tiles and joints between tiles to form holes that reach to the underlying concrete wall, after which resin is injected behind the almost separated tiles through these holes to adhere the tiles to the concrete wall. A small impact drill for drilling concrete, for example, is used to drill holes in such tiles and tile joints.
However, since ordinary impact drills cause the drill to vibrate during drilling and drill while pounding the drilled object in the manner of a hammer, they conversely promote separation of the tiles resulting in the disadvantage of damaging the outer wall. Therefore, a drilling device is used that is provided with a drilling tool, in which a bit is provided on the end of a rod-shaped or cylindrical drill body, and a rotary drive device for rotating this drilling tool around an axis.
In the case of a drilling device of the prior art as shown in the drawing, a rotary shaft attached with a core bit is rotated by lowering the rotating speed with a gear and so forth in order to increase the generated torque obtained at a predetermined output power of the motor. The output power referred to here indicates the output power that can be extracted outside the motor but excluding the loss within the motor. Although this output power is decreased due to friction and so forth during the course of rotation being transmitted by a gear or other rotation transmission mechanism, it is ultimately converted to output power of the drilling device that rotates the core bit. This output power of the drilling device is then supplied for drilling holes.
Namely, if the sum of the force in the tangential direction applied to the end of the core bit due to resistance received from the drilled object during drilling is taken to be Ft, and the radius of the core bit is taken to be r, then the work required for making one revolution of the core bit during drilling can be expressed as 2πrFt. Therefore, when the core bit rotates fN per unit time, the power of the drilling device can be expressed as 2πrFtfN. This relationship is more accurate if expressed as 2πrFtfN=vFt since rω is the peripheral velocity v at the outer periphery of the core bit. However, since rFt is the generated torque required for rotating the core bit, if this generated torque is taken to be T, then the output power of the drilling device can be represented as Poutput∝TfN proportional to the product of rotating speed and generated torque.
In this manner, under conditions in which output power Poutput of the drilling device is a certain fixed value, in order to increase generated torque T, the rotating speed fN of the drilling tool is reduced by lowering the rotating speed of the motor with gears and so forth, even though transmission loss of the output power attributable to the gears is present.
A drilling device of the prior art as previously described had the shortcoming of slow drilling speed. Consequently, it invited the problems of prolonging the construction period and worsening the surrounding environment due to noise and vibrations generated during drilling.
For example, in the case of performing tunnel repair, a large number of holes having a depth of 500-1000 mm must be drilled. However, in the case of using a drilling device of the prior art, it takes about 30 minutes to drill a single hole, thereby resulting in the problem of requiring enormous construction costs in terms of labor costs alone to complete drilling of all the holes.
In addition, construction work has also recently been performed involving not only the concrete walls of tunnels, but also drilling holes in the concrete wall on the inner surfaces of sewer pipes followed by injecting a corrosion-resistant material behind the sewer pipes. In this manner, there has been a need to develop a technology suitable for drilling a large number of holes in a short period of time in concrete walls over long distances.
In addition, since drilling devices of the prior art as mentioned above drill holes while reducing the rotating speed of the drilling tool without using impact vibrations like those used in impact drills, they had the disadvantage of a slow drilling speed as compared with ordinary impact drills. There are cases in which nearly all of the tiles of outer walls are typically separated or beginning to be separated in the case of poorly constructed buildings and so forth. Since the task of completely removing all of the tiles and then reattaching them is actually quite bothersome, resin is ultimately injected behind all of the separated tiles. In this case, an extremely large number of holes must be drilled in the tiles. Consequently, there were the problems of a prolonged construction period and increased costs due to the increase in drilling time. In view of these reasons, there was a desire to develop a drilling device having low levels of vibrations capable of rapidly drilling holes comparable to impact drills and particularly without promoting separation of the tiles due to vibrations generated during drilling.
Therefore, the object of the present invention is to provide a drilling device and drilling method capable of drilling a drilled object in a short period of time by reducing the value of the work required to drill holes of a predetermined depth without waste.